Studies continue on the role of the reticuloendothelial system in the clearance of immune complexes and in the production of autoimmune disease. Particular emphasis has been placed on Fc receptors, their ennumeration, and mechanism of action. Patients with HLA B8 DRw3, earlier shown to have an Fc receptor specific clearance defect by in vivo studies of red cell clearance, have the normal number of Fc receptors on their peripheral blood mononuclear cells. This was shown in studies of rosette formation with both human and rabbit antibody coated red cells and in studies of specific Fc receptor number and affinity using monoclonal human proteins. Thus, the defect in Fc receptor specific clearance cannot be related to a defect in the peripheral blood monocyte at this time. Importantly, a large group of patients with auto-immune hemolytic anemia have been shown to have a marked increase in their cell membrane Fc receptor number with a normal association constant of their receptor protein. On steroid therapy, the receptor number decreases toward normal. The role of glucocorticoids in receptor number and clearance rates is being studied in normal volunteers. Preliminary data suggests that administration of glucocorticoids to normals down regulates Fc receptor number on peripheral blood monocytes.